This invention relates to a blade row group.
The aerodynamic loadability and the efficiency of fluid-flow machines, in particular blowers, compressors, turbines, pumps and fans, is limited by the growth and the separation of boundary layers near and on the hub and casing walls. To remedy this problem in the case of high aerodynamic loading and important boundary layer growth on the annulus duct side walls (hub or casing), the state of the art provides solutions only to a limited extent.
State of the art in fluid-flow machines are arrangements with double-row stator wheels, usually employed as exit stator wheels in compressors, or also double-row rotor arrangements in which directly adjacent rotors operate counter-rotatingly, or in which two directly adjacent rotor blade rows are attached to a common drum. A fluid-flow machine of this type is known for example from EP 2 261 463 A2. With these arrangements, and in particular with those having several, directly adjacent blade rows firmly arranged relative to one another (for example several rotor blade rows on the same drum, or several stator vane rows), severe boundary layer separation occurs at higher aerodynamic loading in the boundary zone of the main flow path, i.e. at the hub or casing contour.
The problems in the edge areas are primarily due to the fact that the favourable arrangement of two adjacent blade edges of a blade row group in the center of the main flow path has an unfavourable effect in the vicinity of the flow path boundary. Also, design rules known from individual blade rows are not applicable. New rules must be devised for blade row groups. In particular, the required flow deflection may quickly be so high either in parts of the blade height or along the entire blade height that the conventional arrangement of a blade row group leads to a separated boundary layer flow in the edge areas of the main flow path on the hub and/or the casing walls.
It is known from US 2013/0209223 A1 to vary the meridional overlap between front and rear blades of a blade row group between the center of the main flow path and the main flow path boundary. From US 2013/0209224 A1 it is known to vary the degree of overlap between front and rear blades of a blade row group as well as the distance of adjacent edges of the front and rear blades between the center of the main flow path and the main flow path boundary.
A variation of the overlap and of the distance is usually obtained with every configuration of a blade row group, without this necessarily having an advantageous effect on the flow. US 2013/0209223 A1 and US 2013/0209224 A1 describe most different possibilities for variation, without using aerodynamically significant parameters. Technical teachings relating to stipulation of the profile depths and the precise shape for all blade edges of two adjacent member blade rows are not provided either, although these are of crucial importance for favourably influencing the overall flow behaviour. US 2013/0209223 A1 deals with the edge spacing of adjacent member blade rows in the meridional plane (machine side view). The flow direction in blade rows has however a sometimes considerable flow swirl component, so that the blading may be considerably inclined relative to the meridional direction. Crucial for the aerodynamic behaviour, however, is a fixing of the blade edges in a view perpendicular and parallel to the blade profile chord. A blade edge visible in the meridional plane can therefore be generated by an infinite number of different blade edge shapes fixed in the aerodynamically relevant chord and chord-orthogonal directions. It cannot therefore clearly describe the shape of the blade edges, and accordingly cannot solve the aerodynamic problem of achieving an advantageous effect on the flow.